1. Field of the Invention
The present invention relates to signal transmission apparatus for transmitting a plurality of rectangular wave signals whose rising or falling edges may occur substantially simultaneously, and to a data processing apparatus including such a signal transmission apparatus.
2. Description of the Related Art
Currently, data processing apparatuses for performing various data processing are utilized in many fields. Such data processing apparatuses are configured in varying forms depending on required performance or use environments. For example, when a data processing apparatus comprising ICs (Integrated Circuit) is used in a particular application, the data processing apparatus may incorporate a unique circuit apparatus as an ASIC (Application Specific IC).
Such ICs are typically configured by digital circuits, but may includes analog circuits. In this case, since the digital circuits perform digital processing and the analog circuits perform analog processing, it is possible to utilize the advantages of both digital operation and analog operation.
However, when a digital circuit produces rectangular wave signals as digital data, rising or falling edges may simultaneously occur in a plurality of rectangular wave signals. Such simultaneous occurrence of rising or falling edges in a plurality of rectangular wave signals produces much noise which is likely to affect analog circuits.
An apparatus which intends to solve such a problem is disclosed, for example in Japanese Patent Laid-open Publication No. 9-23148. FIG. 1 shows the configuration of a conventional signal transmission apparatus disclosed in the gazette.
This conventional signal transmission apparatus 100 comprises, for example, five signal transmission paths 101 to 105 as a plurality of signal transmitting means. Each of signal transmission paths 101 to 105 respectively transmit a rectangular wave signal. The rising and falling edges of these signals may occur substantially simultaneously.
Signal transmission path 101 consists of one simple signal wire, while signal transmission paths 102 to 105 are each connected to delay circuits 117. Signals which are delayed by delay circuits 117 for a predetermined time period are supplied to one terminal of respective selectors 107 to 110 and to four delay circuits 112 to 115 with differing delay times. Signals which are delayed by delay circuits 112 to 115 are supplied to the other terminal of respective selectors 107 to 110.
Each of selectors 107 to 110 selects and outputs either the signal from delay circuit 117 or the signal from the associated delay circuit. Signal transmission paths 101 to 105 are also connected near their input terminals to switching control circuit 116 which in turn is connected to control terminals of selectors 107 to 110.
Switching control circuit 116 counts rectangular wave signals whose rising edges and falling edges occur simultaneously of five rectangular wave signals transmitted through signal transmission paths 101 to 105, and performs control to cause selectors 107 to 110 to select the signal from the associated delay circuit if the count exceeds a predetermined threshold value.
Delay circuits 117 having the same delay time inserted in respective signal transmission paths 102 to 105 serve the delay rectangular wave signal for a time period required for the operations of switching control circuit 116 and selectors 107 to 110.
In the aforementioned conventional signal transmission apparatus 100, signal transmission paths 101 to 105 each transmit a rectangular wave signal. In the transmission, signal transmission path 101 transmits a rectangular wave signal without delay, while signal transmission paths 102 to 105 transmit rectangular wave signals after the signals are delayed as required.
Next, the operation of conventional signal transmission apparatus 100 is described.
When a rectangular wave signal is transmitted through respective signal transmission paths 101 to 105, switching control circuit 116 counts the number of the simultaneous occurrence of rising and falling edges in the signals. If the counted number is below the predetermined threshold value, then switching control circuit 116 causes selectors 107 to 110 to select the normal paths into which delay circuits 112 to 115 are not inserted. Thus, the rectangular wave signals are transmitted over signal transmission paths 102 to 105 without being delayed by delay circuits 112 to 115.
However, if the number of the simultaneous occurrence of rising edges and falling edges in the five rectangular wave signals exceeds the predetermined threshold value, then switching control circuit 116 causes selectors 107 to 110 to select the paths into which delay circuits 112 to 115 are inserted.
Each of rectangular wave signals in signal transmission paths 102 to 105 is then delayed by delay circuits 112 to 115 for differing time periods. This causes rising edges and falling edges in the plurality of rectangular wave signals to occur in different timings, thereby preventing the occurrence of noise due to the simultaneous rising or falling of many signals.
Some digital circuits which output rectangular wave signals to the aforementioned signal transmission apparatus 100 and some digital circuits which receive rectangular wave signals from signal transmission apparatus 100 allow switch the setting of operational speeds.
However, in the aforementioned conventional signal transmission apparatus 100, since delay circuits 117 are interposed in signal transmission paths 102 to 105, each of rectangular wave signals is always delayed by delay circuit 117 for a predetermined time period regardless of the operations of switching control circuit 116 and each of selectors 107 to 110. Furthermore, a delay time in delay circuit 117 is fixed, so that conventional signal transmission apparatus 100 cannot appropriately correspond to switching of the setting of the operational speed of a digital circuit.
For example, if the delay time in signal transmission apparatus 100 is designed to correspond to the low-speed operation of a digital circuit, the transmission of digital data will be uselessly delayed when the digital circuit is operated at high speed. On the other hand, if the delay time in signal transmission apparatus 100 is adapted to the high-speed operation of the digital circuit, the operation of delaying digital data will be late when the digital circuit is operated at low speed.
In view of the aforementioned problems, it is an object of the present invention to provide signal transmission method and apparatus which, when at least some of a plurality of rectangular wave signals are delayed for differing time periods to prevent the occurrence of noise, allows the setting of the delay time appropriately for the operational speed of a digital circuit.
The signal transmission apparatus according to the present invention comprises a plurality of signal transmitting means, a plurality of signal delaying means, and time varying means. With such a signal transmission apparatus, when the plurality of signal transmitting means each transmits a rectangular wave signal, rising or falling edges of these rectangular signals may occur substantially simultaneously, at least some of the plurality of rectangular wave signals transmitted by the plurality of signal transmitting means are delayed by the signal delaying means for differing time periods. Thus, the occurrence of noise due to the simultaneous rising or falling of many rectangular wave signals is prevented. In addition, the delay time in each of the plurality of signal delaying means is set by the time varying means based on the operational speed of a digital circuit which outputs digital data as rectangular wave signals.
In another aspect of the present invention, each of the plurality of signal delaying means comprises a predetermined number of delay circuits, and the time varying means may comprise a plurality of selectors each selecting one delay circuit among the predetermined number of delay circuits. This arrangement allows the variable setting the delay time in each of the plurality of signal delaying means.
In another aspect of the of the present invention, each of the plurality of signal delaying means also includes one direct path for transmitting the rectangular wave signal without delay, and the selector of the time varying means may select the direct path in addition to the delay circuits in each of the plurality of signal delaying means. In this case, since the selector of the time varying means selects one of the plurality of delay circuits or the one direct path in each of the plurality of signal delaying means, the rectangular wave signal is transmitted without delay when the direct path is selected.
A data processing apparatus of the present invention comprises a digital circuit, an analog circuit, and the signal transmission apparatus of the present invention. The digital circuit performs data processing with digital data, and the analog circuit performs data processing with analog data. Since the digital circuit produces a plurality of rectangular wave signals as digital data and outputs the signals to the signal transmission apparatus of the present invention, at least some of the plurality of rectangular wave signals transmitted by the signal transmission apparatus are individually delayed for differing time periods. At this point, since the digital circuit controls time settings the time varying means in the signal transmission apparatus, the delay time in the signal transmission with the signal transmission apparatus are also controlled by the digital circuit which produces the rectangular wave signals.
In another aspect of the present invention, the digital circuit may comprise speed varying means for variably setting the operational speed thereof and setting control means for controlling time settings with the time varying means based on the operational speed set by the speed varying means.
In this case, the speed varying means sets the operational speed of the digital circuit, and the setting control means controls the time settings with the time varying means based on the operational speed set by the speed varying means.
It should be noted that various means referred to in the present invention may be realized in various forms such as dedicated hardware, computers provided with proper functions through programs, functions realized within computers with proper programs, a combination thereof, and the like.
The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.